public class Test {
    /*
    替换所有的问号
    class Solution {
    public String modifyString(String s) {
        char[] arr = s.toCharArray();
        for(int i = 0 ; i < arr.length; i++) {
            if(arr[i] == '?') {
                for(char ch = 'a'; ch <= 'c'; ch++) {
                    if((i == 0 || ch != arr[i-1]) && (i == s.length()- 1 || ch != arr[i+1]))
                        {
                            arr[i] = ch;
                            continue;
                        }
                }
            }

        }


        return new String(arr);
    }
}
    幂集
    class Solution {
    List<List<Integer>> ret = new ArrayList<>();
    List<Integer> path = new ArrayList<>();

    public List<List<Integer>> subsets(int[] nums) {
        dfs(nums, 0);
        return ret;
    }

    void dfs(int[] nums, int index) {
        if (index == nums.length) {
            ret.add(new ArrayList<>(path));
            return;
        }
        // 不选
        dfs(nums, index + 1);
        // 选
        path.add(nums[index]);
        dfs(nums, index + 1);
        path.remove(path.size() - 1);

    }

}
     */
}
